1. Field of the Invention
The present invention relates to a string instrument such as violin, viola, cello, or the like which can produce a stable amount of sounds in a low sound region as well as in a high sound region.
2. Description of the Prior Art
A conventional string instrument, for example, a violin is basically constructed in the following manner. Referring to FIG. 1, a violin 1a is mainly formed of a body 2 in the shape of gourd and a neck 3 attached to the body 2. Four strings 6 are stretched between pegs 4 attached to the neck 3 and a tailpiece attached on the body 2. These strings 6 are supported by a bridge 7. A bow 8 is slid on these strings 6 to produce sounds. More specifically, referring to FIG. 2, the body 2 of the violin 1a is made up of a top plate 9, a bottom plate 10 and side plates 11 for coupling the top and bottom plates 9, 10. The top plate 9 is provided on the rear surface thereof with a bass-bar 12 which serves as a reinforcement to prevent buckling from occurring due to a compression load caused by a tension of the strings 6. A sound-post 13 is further provided between the top plate 9 and the bottom plate 10 such that the bridge 7 is located substantially above the sound-post 13.
As a playing place has changed from a personal hole in the medieval ages to a public concert hole in the present days, it has been required to increasingly produce larger sounds. However, the basic structure of the violin la as described above has not been changed from the era of Antonio Stradivarius for about 300 years except that the tension of the strings 6 was necessarily higher and the bass-bar 12 was provided as reinforcement.
The violin 1a constructed as described above is also considered as a sound generating or audio instrument. A sound range of the violin la involves four octaves and extends from 196 C.P.S. to 3136 C.P.S as shown in FIG. 3. An audio instrument has three elements: a vibrating section, a transmitting section for. transmitting the vibration, which also includes a resonance system and a filter system in addition to a transmission system, and a radiating section for radiating sound wave to the air. Comparing these elements to the constituents of the violin 1a, the strings 6 correspond to the vibrating section; the bridge 7 to the transmission system and the filter system; air in the body 2, the top plate 9 and the bottom plate 10 to the resonance system; and the top plate 9 to the radiating section. Thus, since the performance of the violin 1a may be considered in the same manner as that of a normal audio instrument, the performance may be classified into (1) frequency characteristics; (2) sound quality (spectrum); (3) transient characteristics; (4) efficiency; and ( 5) directivity.
In these characteristics, the frequency characteristics were measured for four conventionally constructed violins as shown in FIG. 4. Specifically, an oscillator 14 was connected to a side face of the bridge 7 through an amplifier 15, from which sound as an elastic wave was sent to the violin 1a. This sound was transmitted from the bridge 7 through the top plate 9, the sound-post 13, the bottom plate 10, the body 2 and air to produce sounds by vibrations of these elements which were picked up by a microphone located seven centimeters above the bridge 7. Also, its sound pressure was measured by an oscillograph 18 through an amplifier 17. The results of the measurement show that the four violins respectively present a response curve substantially as illustrated in FIG. 5. More specifically, the response curve indicates a tendency that a peak distance is wide in a low sound region, and the sound pressure is low, that is, the sound is feeble in a high sound region.
In other words, in the conventional violin 1a, while the amplitude of the top plate 9 is large in the low sound region as shown in FIG. 5, the peak distance is wide, so that sound on G line remote from the peak presents a week fundamental tone. To prevent this, the frequency range of the response curve may be extended to the lower region as much as possible. To achieve this, the resonance frequency of the top plate 9 may be lowered as much as possible. The resonance frequency f of the top plate 9 is given by the following equation: ##EQU1## where h represents the thickness of the top plate; E the Young's modulus of elasticity; .mu. the Poisson's ratio; .rho. the specific gravity of the top plate; and K a constant.
It will be understood from the above equation that, without considering the specific gravity of the top plate, a thinner top plate results in shifting the frequency band of the response curve in the lower direction and simultaneously reducing the sharpness of the peak.
However, since the top plate, generally plane and symmetric, always presents a constant frequency ratio between harmonics, reduction of the thickness of the top plate causes the harmonics to simultaneously shift in the lower direction, thereby narrowing the frequency band as a whole. This results in a decrease of the sound amount in the high sound region and generation of dull tone color as a whole. This coincides with an empirically obtained fact that a thinner top plate causes unclear sound.